Basically 0 oil pressure idle, perfect when driving !?!

Matt930 · 11-11-2013, 02:36 PM

Hi Guys,

I'm a little lost on this one. Basically when the car is cold, it idles with oil pressure against the bypass spring (75 odd PSI), but as it comes right up to temperature it drops to basically 0.4 bar

Even if I've been belting the **** out of it and its quite 'warm', it still does meet the 10PSI / Thousand Minimum, but at idle there really is basically nothing when it gets this hot...

Engine doesn't knock, rattle or make any noises, its never let me down or other wise to make me think it is actually a block issue. I've changed the Oil Pressure Sender unit, its fine. Its also idling a little low at the moment, so maybe that's not helping.

I will try ripping out the pressure relief valves next weekend when I'm doing my new oil cooler and hopefully there is something wrong with the pistons there. But I wanted to ask does anyone think that it might be a oil pump?

Its basically like it works fine in operation, but at idle, the pump efficiency is just not there... Anyway, thoughts would be appreciated.

Matt

Tt surgeon · 11-11-2013, 03:27 PM

If you're low on oil it could show low at idle.

Matt930 · 11-11-2013, 04:10 PM

Unfortunately not, its square in the middle of the gauge warm...
Thanks for the idea though

porche · porche's Garage

Even though the oil level gauge is at the mid-point when warm, check the oil level when warm using the dip stick to reconfirm the gauge accuracy. As Tt stated, you just may be low on oil. If not, maybe it’s the oil pressure sensor, oil pressure gauge or wiring between the two.

torresmd · 11-11-2013, 04:50 PM

Where is your car at idle? try raising the idle just a tad and see if that helps.

full quack · 05:39 PM

Um...1 bar is equal to 14.7 psi, not 10psi.

All of these cars show scary low pressure readings on the factory gauge, at idle with the oil at full temp.

How long have you owned your 930?

I see that you have only 3 posts, so I'm assuming you might be new to this 930 game. Do you realize that these cars have a semi-dry sump oiling system?

Is this low idle oil pressure, something new for your car, or are you just now noticing it?

Curious minds want to know..

Mark

Matt930 · 11-11-2013, 05:51 PM

Hey all,
Thanks for the help.

Yeah, I knew about the 1 bar not equaling 10PSI thing, but many posts on here (well from my research - didn't want my first post to make me look like a goose) 10-15PSI / 1000 RPM to be 'acceptable'.

Owning the car wise, its been about 2 years. Its always done it, and the driving oil pressure has always been fine, but i also didn't use it that regularly, as there were a lot of other things that needed attention. I've got the most of them sorted now, and keen to start driving it more, so figured that i better get this sorted.

I work with Common Rail Diesel Pumps quite a bit, and thought that this very low pressure at low RPM, fine at high RPM looked very much like a pump leakage problem and therefore maybe someone else had found the same thing...

Anyway, i really only started to worry about it after a meeting on the weekend with a few other 930s, some of which were 2bar at idle quite warm... When I've really been giving it some, I'm luck if I've got 0.2Bar (idle is a little under 500 At the moment but). Maybe I should just start here and take it from there...

turbo ride · 11-11-2013, 05:58 PM

Get your idle up to spec - then I'd be curious what your idle oil pressure is. My car idles nice right around 900.

full quack · 11-11-2013, 06:02 PM

< than 500 RPM for an idle...oh my...there in lies your main problem!

You need to raise that up to about 950 rpm, to have a happy car.

Sheezzz mine won't even idle that low.

Mark

mooney265 · mooney265's Garage

Mine idles at a smooth 250, when cold [no AAV] - - sounds awesome with the Zork. It quickly goes up to 950 when warm...

Back on subject: yes, need idle up to 950 when warm, or low oil pressure will be the result...

spuggy · 11-13-2013, 06:17 AM

Quote:

Originally Posted by Matt930

Hi Guys,

I'm a little lost on this one. Basically when the car is cold, it idles with oil pressure against the bypass spring (75 odd PSI), but as it comes right up to temperature it drops to basically 0.4 bar

Even if I've been belting the **** out of it and its quite 'warm', it still does meet the 10PSI / Thousand Minimum, but at idle there really is basically nothing when it gets this hot...

Engine doesn't knock, rattle or make any noises, its never let me down or other wise to make me think it is actually a block issue. I've changed the Oil Pressure Sender unit, its fine. Its also idling a little low at the moment, so maybe that's not helping.

I will try ripping out the pressure relief valves next weekend when I'm doing my new oil cooler and hopefully there is something wrong with the pistons there. But I wanted to ask does anyone think that it might be a oil pump?

Its basically like it works fine in operation, but at idle, the pump efficiency is just not there... Anyway, thoughts would be appreciated.

Matt

What year 930?

Pre-78 930's don't have the bigger oil pump the later cars got. So oil pressures more like 911's of the same era are normal. And that sounds like what you're seeing.

If my '78 showed pressures like you describe, I wouldn't be running it, let alone driving it.

Matt930 · 11-13-2013, 12:55 PM

Bang on the money there Spuggy;

She's a 1976.

I've bumped up the idle to 950-1000rpm, oil pressure is more like 10Psi, and 6-8 when really hot, but from what i figure, these older earlier cars, this is 'somewhat' normal (albeit a little on the lower side).

I very may just up-spec the oil pump in the coming christmas break anyway. time for some more research.

HFR_Racer · HFR_Racer's Garage

Did you check your oil pressure with a mechanical gauge to double-check against your oil pressure sending unit?

porche · porche's Garage

Great thread! Learned 2 things;
- 1 bar oil p needs 950rpm
- '78 up has bigger oil pump

spuggy · 12:42 PM

Quote:

Originally Posted by Matt930

Bang on the money there Spuggy;

She's a 1976.

Yah, I didn't even think about it when I replied, but looking back the fact you quoted PSI was a clue. I have the numbered oil pressure/temp gauges in my '77 too. Love 'em...

Quote:

I very may just up-spec the oil pump in the coming christmas break anyway. time for some more research.

930 pumps are very spendy now. Also NLA, I believe. The factory went in a different direction with the later high-perf pumps - e.g. for the GT cars, which I believe is the superceding replacement part. IIRC, they have less flow, but more scavenge.

Check the engine rebuild forum for detailed discussions/fitment info, but you'll probably need to clearance the early case to fit a bigger pump. Don't think that's a precision job exactly - although re-assembling the case takes some skills, of course.

If the 3.0 crank uses the same 9mm rod bolts the 3.3's got, upgrade to ARP as a matter of course at the first opportunity would be my advice.

spuggy · 11-15-2013, 12:41 PM

Quote:

Originally Posted by full quack

Um...1 bar is equal to 14.7 psi, not 10psi.

Yup.

Quote:

All of these cars show scary low pressure readings on the factory gauge, at idle with the oil at full temp.

My 3.3 shows about 20-25 PSI on the factory gauge at idle with the oil at full temp. But it's set to idle at 1050, because it prefers that with the SC cams and my cam/ignition timing - idle can be pretty lumpy otherwise...

Pretty sure the 74-77 930's got the exact same pump as the middie 911's - e.g. bigger than earlier cars. I've read that the 60's cars can light the oil pressure idiot lamp at idle when hot, and that's considered "normal" for them, on a "so long as it goes out when you rev it" basis. That's also expected for the 2.0 924. Don't know if the 911 got a pump upgrade between the 60's and the middies - don't remember noticing one.

Could be wrong, but I seem to recall that the idiot sensor trips at 6 PSI....